This is a game of polo, played on horseback. You move your horse with the joystick. The mallet swings automatically and will always send the ball in the direction of the opposing goal. The object is simply to to get the ball through the opposing player's goal more than they get the ball through yours. Some game variations have the ball wrap around the screen, some make the ball bounce off the sides, some give each player one horse to control, some two apiece.
Description courtesy of MobyGames
via a CC license